The present invention relates generally to semiconductor lasers. More particularly, the present invention relates to optically pumped semiconductor lasers.
Semiconductor lasers have become more important. One of the most important applications of semiconductor lasers is in communication systems where fiber optic communication media is employed. With growth in electronic communication, communication speed has become more important in order to increase data bandwidth in electronic communication systems. Improved semiconductor lasers can play a vital roll in increasing data bandwidth in communication systems using fiber optic communication media such as local area networks (LANs), metropolitan area networks (MANs) and wide area networks (WANs). A preferred component for optical interconnection of electronic components and systems via optical fibers is a semiconductor laser known as a vertical cavity surface emitting laser (VCSEL). The current state of design and operation of VCSELs is well known. Due to optical properties of optical fibers, photons emitted at longer wavelengths from a laser tend to propagate longer distances and are less disturbed by optical noise sources. Thus, forming a VCSEL that can operate at longer wavelengths, such as a wavelength greater than 1.25 xcexcm, is desirable.
Lasers can be excited or pumped in a number of ways. Typically, VCSELs have been electrically excited (electrically pumped) by a power supply in order to stimulate photon emission. However, achieving photon emission at long wavelengths using electrical pumping has not been commercially successful due to a number of disadvantages. Presently, there is no viable monolithic electrically pumped long wavelength VCSEL solution for practical applications. It is desirable to use an Indium-Phosphide semiconductor substrate for long wavelength VCSEL operation. However, there is no monolithic semiconductor distributed Bragg reflector (DBR) which can lattice match with an Indium-Phosphide substrate and provide a large enough difference in index of refraction for reflecting a laser beam. Lattice matching is important in order to maintain laser material growth dislocation-free. Alternatives have been proposed and demonstrated with limited success. One solution is to wafer bond an Indium-Phosphide based active material system with a Gallium-Arsenide/Aluminum-Gallium-Arsenide (GaAs/AlGaAs) DBR. While constant wave (CW) operation of up to 70 degrees centigrade has been achieved, the output power is too low for the device to be of any use.
More recently it has been shown that a VCSEL can be optically excited (optically pumped) to stimulate photon emission. Referring now to FIG. 1, it has been shown that an in-plane laser 100 can have its emitted photons 101A redirected by a mirror 102 into the direction of photons 101B for coupling into a VCSEL 106. The in-plane laser 100 is designed to be electrically excited in order to emit photons 101A at relatively short wavelengths (850 nanometers (nm) to 980 nanometers (nm)). The redirected photons 101B from the in-plane laser 100, also having relatively short wavelengths, optically excite the VCSEL 106. The VCSEL 106 is designed to be optically excited in order to emit photons 108 at relatively long wavelengths (1250 nm to 1800 nm). A disadvantage to the system of FIG. 1 is that its components are not integrated together. In U.S. Pat. Nos. 5,513,204 and 5,754,578 by Vijaysekhar Jayaraman (referred to as the xe2x80x9cJayaraman Patentsxe2x80x9d) it is shown how to integrate an electrically pumped short wavelength VCSEL together with an optically pumped long wavelength VCSEL. However, there are a number of disadvantages to the integrated solution offered by the Jayaraman Patents. One problem with using an electrically pumped short wavelength VCSEL to optically pump a long wavelength VCSEL is that enormous heat is generated in the electrically pumped short wavelength VCSEL due to electrical current injection. The heat generated by the electrically pumped VCSEL can not be dissipated efficiently which then is coupled into the long wavelength VCSEL increasing its junction temperature such that it can not lase efficiently. Another disadvantage is that the electrical resistivity is high because the electrical contact area in the electrically pumped short wavelength VCSEL is relatively small, and the current has to go through many layers of resistive p-type doped DBR. Another disadvantage in using an electrically pumped VCSEL is that the thermal resistance is high because of a restricted heat flow path. The small carrier confinement region in an electrically pumped VCSEL causes heat to accumulate in a small area from which it is difficult to dissipate. Another disadvantage is that the output power from an electrically pumped short wavelength VCSEL is limited, which negatively impacts the output power from the optically pumped long wavelength VCSEL as well. The integrated solution of the Jayaraman Patents can not provide sufficient power to meet a data link module specification of providing a constant wave power output at eighty degrees Centigrade. Another disadvantage is that the cost of manufacturing the two VCSELs as proposed in the Jayaraman Patents is relatively high.
It is desirable to overcome the limitations of the prior art.
Briefly, the present invention includes a method, apparatus and system as described in the claims. An integrated optically pumped vertical cavity surface emitting laser (VCSEL) is formed by integrating an electrically pumped in-plane semiconductor laser and a vertical cavity surface emitting laser together with a beam steering element formed with the in-plane semiconductor laser. The in-plane semiconductor laser can be a number of different types of in-plane lasers including an edge emitting laser, an in-plane surface emitting laser, or a folded cavity surface emitting laser. The in-plane semiconductor laser optically pumps the VCSEL to cause it to lase. The in-plane semiconductor laser is designed to emit photons of relatively short wavelengths while the VCSEL is designed to emit photons of relatively long wavelengths. The in-plane semiconductor laser and the VCSEL can be coupled together in a number of ways including atomic bonding, wafer bonding, metal bonding, epoxy glue or other well know semiconductor bonding techniques. The beam steering element can be an optical grating or a mirrored surface. A number of embodiments of the integrated optically pumped vertical cavity surface emitting laser are disclosed.